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  #1  
Old 05-07-2018, 07:12 PM
StressedOut StressedOut is offline
 
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Location: Fullerton, CA
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Default HS Inspar Rib Holes

The six HS-1004 ribs all have holes oriented vertically in the middle of the rib. However, it looks like only the two inboard ribs (L/R) use them to attach to the HS-00916 stringer web. See page 08-01.

I want to confirm these holes are not used for anything else later in the plans. I've looked forward to Section 11 (Empennage Attach) and see nothing there.

It's generally a good practice to fill open holes with a rivet for fatigue reasons. I want to fill those holes, but need some confirmation they aren't otherwise used.
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  #2  
Old 05-08-2018, 09:22 AM
Aluminum Aluminum is offline
 
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Quote:
Originally Posted by StressedOut View Post
The six HS-1004 ribs all have holes oriented vertically in the middle of the rib. However, it looks like only the two inboard ribs (L/R) use them to attach to the HS-00916 stringer web. See page 08-01.

I want to confirm these holes are not used for anything else later in the plans. I've looked forward to Section 11 (Empennage Attach) and see nothing there.

It's generally a good practice to fill open holes with a rivet for fatigue reasons. I want to fill those holes, but need some confirmation they aren't otherwise used.
An authoritative answer to this would require the kind of structural analysis only Van's engineers are qualified to perform.

My $.02: material this thin gets wrinkled even by -3 rivets properly driven, which will transfer loads elsewhere etc. It's a critical area that has been significantly beefed up compared to the older RV models. I say leave good enough alone since it's not called out in the plans.
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  #3  
Old 05-08-2018, 09:26 AM
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Mike S Mike S is offline
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Are these holes possible tooling alignment holes??
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  #4  
Old 05-08-2018, 01:39 PM
StressedOut StressedOut is offline
 
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Quote:
Originally Posted by Mike S View Post
Are these holes possible tooling alignment holes??
Mike,

They don't appear to be alignment holes. Those holes are used to attach the HS-00916 stringer web to the HS-1004 inspar rib in only two locations. Vans uses the same part on the two inspar ribs outboard of the stringer web (four total ribs), but the web only spans the two on either side of the centerline.

The overview drawing of the HS on page 08-01 shows holes at the web/rib interface, but no holes on the other identical ribs. I wish they would have not punched some or all of those holes for us in this case. I'd rather match drill them.

Quote:
Originally Posted by Aluminum View Post
An authoritative answer to this would require the kind of structural analysis only Van's engineers are qualified to perform.

My $.02: material this thin gets wrinkled even by -3 rivets properly driven, which will transfer loads elsewhere etc. It's a critical area that has been significantly beefed up compared to the older RV models. I say leave good enough alone since it's not called out in the plans.
Dan,

I agree that the specific static loads and load spectra would only be available to Vans engineers, however, this particular issue doesn't require that information. Good engineering practice for large transport aircraft dictates open holes are filled with a rivet to lessen the possibility of a crack forming at the hole. Rivets put compressive stress in the holes which gives significantly better protection from crack initiation. I've seen a number of cracks in the fleet (big planes, not Vans) where the crack initiated at an open hole. I've been involved in creating service bulletins to inspect for and fix such issues.

You bring up a good point about possible wrinkling of 0.025 in. sheet. Before I put in extra rivets I'll test it out on some scrap of the same thickness. If it wrinkles then I could fabricate a small doubler, or, more likely, just forget about filling the holes.

But first I need confirmation that these four ribs do not use those holes for anything.
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RV-14A Kit#140433
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  #5  
Old 08-22-2018, 07:59 AM
TASEsq TASEsq is offline
 
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Hi art,

Reading ahead and about to start my HS.

What did you end up deciding to do here?
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  #6  
Old 08-22-2018, 01:35 PM
StressedOut StressedOut is offline
 
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Trent,

In the end I left the holes alone and unfilled with rivets. The middle of the HS-1004 ribs buried inside the stab can be inspected through the lightening holes in the rear spar, albeit with some difficulty. When it comes time to compile a list of inspections for the annual condition inspection, this area will be included out of an abundance of caution. It's highly likely the operating loads in the rib aren't high enough or frequent enough to start a crack around the holes.

Looking at the drawings, I think the reason for Vans deciding to punch the holes has to do with the difficulties of match drilling the two inboard HS-1004 ribs to the HS-00916 stringer web. I couldn't figure out a simple, easy way to align them when you're assembling the stringer web assembly without those holes. If you don't get the web holes placed correctly you affect the alignment of the stringer holes to the skin. Everything in aircraft design is a compromise between cost, maintainability, performance, manufacturability, etc. Vans puts out an excellent product and I'm sure they felt this was the best way to go.

I'm probably being overly cautious and I'm sure it's because of my day job. What's good for a big airliner is not necessarily required for a small EAB plane. My challenge is to figure out the differences.
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Art Jackson
RV-14A Kit#140433
Completed: Vertical Stab/Horizontal Stab
Scrapped: Rudder
Working on: Empennage (Elevator)
Construction log - mykitlog.com/ajackson
Dues paid on 2 November 2017
Member of EAA Chapter 92 (KCNO)
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  #7  
Old 08-22-2018, 09:39 PM
TASEsq TASEsq is offline
 
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No worries - appreciate the follow up
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